1. Field of the Invention
The present invention relates to a viscous fluid type heat generator in which a viscous fluid is subjected to a shearing action or stress in a heat generating chamber to generate heat that is in turn transferred to a heat exchanging fluid circulating through a heat receiving chamber to be carried by the heat exchanging fluid to a desired area to be heated. The present invention may be embodied, for example, as a supplementary heat source incorporated in a vehicle heating system, but it will be appreciated that it is also useful in other applications.
2. Description of the Related Art
Viscous fluid type heat generators used as supplementary heat sources incorporated in a vehicle heating system are known in the art. For example, Japanese Unexamined Patent Publication (Kokai) No. 2-246823 (JP-A-2-246823) discloses such a viscous fluid type heat generator. In this viscous fluid type heat generator, a front housing and a rear housing are combined and fastened together with through bolts, to define therein a heat generating chamber and a heat receiving chamber arranged outside the heat generating chamber to surround the same. The heat generating chamber is isolated from the heat receiving chamber by a partition wall through which heat is exchanged between a viscous fluid in the heat generating chamber and a heat exchanging fluid in the heat receiving chamber. The heat exchanging fluid is circulated and introduced through an inlet port into the heat receiving chamber and delivered through an outlet port from the heat receiving chamber to an external heating circuit.
A drive shaft is supported for rotation by a bearing in the front housing, and a rotor element is fixedly mounted on the drive shaft to be rotatable within the heat generating chamber. The rotor element includes outer faces arranged face-to-face with the inner wall surfaces of the heat generating chamber to define therebetween small gaps in the shape of labyrinth grooves. The viscous fluid, such as silicone oil, is supplied into the heat generating chamber to fill the small gaps between the outer faces of the rotor element and the inner wall surfaces of the heat generating chamber. The small gaps shaped as labyrinth grooves are uniformly defined in a radial direction of the heat generating chamber and of the rotor element.
When the output torque of the vehicle engine is transferred to the drive shaft of the viscous fluid type heat generator to rotationally drive the drive shaft, the rotor element is also rotated within the heat generating chamber. At this time, the rotating rotor element provides a shearing action or shearing stress to the viscous fluid held in the small gaps between the inner wall surfaces of the heat generating chamber and the outer faces of the rotor element, whereby the viscous fluid generates heat. The generated heat is then transferred through the partition wall from the viscous fluid to the circulating heat exchanging fluid, and the heat exchanging fluid carries the transferred heat to the heating circuit of the vehicle heating system to heat a passenger compartment.
In the above-mentioned conventional viscous fluid type heat generator, the small gaps between the inner wall surfaces of the heat generating chamber and the outer faces of the rotor element are shaped as labyrinth grooves, and thus serve to increase a total heat transferring surface area of the inner wall surfaces of the heat generating chamber and to improve, in some degree, a heat transfer efficiency through the partition wall between the heat generating chamber and the heat receiving chamber. However, since the small gaps shaped as labyrinth grooves are uniformly defined in a radial direction of the heat generating chamber, the heat of the viscous fluid especially held in the outer peripheral region of the small gaps, which tends to rise up to the relatively high temperature, cannot be sufficiently and effectively transferred through the partition wall to the heat exchanging fluid in the heat receiving chamber. As a result, the temperature of the viscous fluid held in the small gaps in the heat generating chamber rises to an extremely high level, so that the degradation of the viscous fluid is accelerated, which in turn results in the reduction of heat generation accomplished by the conventional viscous fluid type heat generator.